Hi,
I'd agree with the above, the image does look a little flat.
This image has lost the subtle and often earthy colours that Venice offers, particularly so on the buildings, but has not replaced them with nice contrast and deep shadows that a good B&W print would offer. Instead all the colours that look similar have turned to various shades of grey, the result is an image with no 'punch'; as said above it is one where the B&W appears as an afterthought.
On a side note, and I know it is difficult in a location such as Venice where I've shot myself, this image would be a lot better without the people in a midground. In this case, I'd have waited until the path was clear before taking the photo, I know this means I've had to wait for an hour or so in some cases, but it's worth it for the right shot.
Hope this helps,
Steve